Electrostriction Devices and Methods for Assisted Magnetic Navigation

ABSTRACT

An apparatus and method for interventional navigation within a subject&#39;s body is provided in which a medical device having at least one electrostrictive element is adapted to cause the distal end of the medical device to bend in a given direction for improving navigation. The medical device may further comprise at least one magnetically responsive element on the distal end, which may be oriented in the approximate direction of a magnetic field that is applied to the subjects body. At least one method for navigating a medical device though a subject&#39;s body is provided, by changing the direction of an applied magnetic field to align a magnetically responsive element on the distal end for orienting the distal end, and by applying a voltage to at least one electrostrictive element disposed in the distal portion of the device for causing the distal end to change orientation from that achieved by application of the magnetic field alone.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/817,063, filed Jun. 28, 2006. The disclosure ofthe above-referenced application is incorporated herein by reference.

FIELD OF THE INVENTION

The present disclosure relates to navigation of medical devices within asubject's body, and more particularly to the use of electrostrictivecomponents in magnetically navigable medical devices.

BACKGROUND OF THE INVENTION

A variety of techniques are currently available to physicians forcontrolling elongate medical devices such as catheters, endoscopes andother surgical tools within a patient. For example, magnetic steeringtechniques provide computer-assisted control of a catheter tip whileallowing an operating physician to remain outside the operating roomx-ray field. In such systems, there is often a lag between the directionof an applied magnetic field and the actual orientation of the distalend of the medical device that must be taken into account fornavigation. Typically, the physician will advance the device only oncethe distal end of the medical device is in the desired orientation,which magnetic steering techniques may not always achieve by themselves:the applied torque might not be sufficient to overcome resistance, asfor instance in areas of rapid blood flow; proximal device advancementmight be ineffective due to device prolapse or buckling at a vesselbranch. Further, magnetic navigation might not prevent dislodgment, forinstance when a guide catheter has been inserted to a coronary ostium,and an interventional device is advanced past the guide catheter distalend; resistance to advancement might cause the guide catheter to becomedislodged, and at the present time it is not possible to preciselycontrol the magnetic field applied at the ostium when magneticallynavigating the interventional device distal tip beyond the guidecatheter distal tip. In endocardial applications using current magneticnavigation technologies, it might be difficult to maintain contactbetween an interventional device distal end and the moving heart wall,in particular upon oblique or glancing approaches where the distal endis not perpendicular to the tissue. U.S. Pat. No. 6,679,836 issued toCouvillon and assigned to SciMed Life Systems, Inc., describes a guidecatheter apparatus comprising a plurality of electro-active polymeractuators disposed along its length, and methods of using the same;however that patent does not teach nor suggest the combinative use ofelectrostrictive materials with magnetic navigation. Similarly,published U.S. patent application No. 20050256398, filed by Hastings etal., describes methods and systems for interventional medicine,including the use of electrostriction to bend a medical device orselectively stiffen a medical device. Although that patent applicationdoes describe methods of magnetically navigating an interventionalmedical device, it does not teach nor suggest the combinative use ofelectrostriction with magnetic navigation. Combinative use of theseapproaches, as disclosed below, significantly improves upon thestate-of-the-art and enables applications that could not have beensuccessfully performed before.

Another motivation for the present invention is the possibility ofimproving the performance of a magnetic navigation system while reducingits size and cost. For example, reducing the size of the magnetic sourcemagnets, made possible by electrostrictive torques applied at particularangles, could provide greater imaging and physician access. For example,the tip force required in certain ablation procedures in the heart, maybe limited by the size of the source magnets, and can be improved by theaddition of electrostriction.

SUMMARY OF THE INVENTION

The present invention relates to medical devices having one or moreactuators for bending or stiffening specific portions of the medicaldevice for enhancing methods of magnetic navigation within a subject'sbody. In the various embodiments, devices and methods for magneticnavigation of a medical device within a subjects body are provided thatemploy electrostrictive behavior. In a first embodiment of a medicaldevice, the device includes at least one electrostrictive elementdisposed on or near its distal end that is adapted to cause the distalend to bend in a given direction. The medical device further comprisesat least one magnetically responsive element on the distal end, whichmay be oriented in the direction of an externally applied magneticfield.

In another aspect of the present invention, various embodiments of amethod for magnetically navigating medical devices including at leastone electrostrictive element are provided. In one embodiment of amethod, the medical device may be magnetically navigated though asubject's body by changing the direction of an applied magnetic field,and by applying a voltage to at least one electrostrictive elementdisposed on or near the distal end to cause the distal end to changeorientation from that achieved by application of the magnetic fieldalone. In another embodiment, a method is provided in which the medicaldevice may be selectively stiffened by applying a voltage to at leastone electrostrictive element on the device while simultaneouslymagnetically orienting the device distal end. In yet another embodiment,a method of magnetically navigating a medical device having a pluralityof electrostrictive elements and a plurality of force or pressuresensors is provided. The pressure sensors enable sensing contact along aportion of the medical device with a tissue surface within the subject'sbody, such that select electrostrictive elements disposed along themedical device may be actuated in response to sensor activity forlocally stiffening or bending the medical device. The method providescontrolling an electrostriction-actuated elongate medical device byactuating one or more of the electrostrictive elements in response to asignal from a contact sensor. Accordingly, methods of magneticnavigation are described that minimize medical device deflection causedby contact with a tissue surface, or enhance the deflection of themedical device for reaching or contacting a target area within thesubjects body, or improve other aspects of navigation within a subject'sbody.

A still further aspect of this invention is the inclusion of methods ofdetermining positions and angles at which a device magnetic tip requiresmagnetic torques which are most difficult to provide by a magneticsystem alone. It is known that certain locations of a device tip, andfor certain initial angles, combined with the need for certain finalturn directions, in addition to the need for larger tip force, becomethe limiting conditions that require stronger and larger source magnets.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1-A is a system block-diagram of a magnetic navigationinterventional system for use of an electrostriction-assistedinterventional medical device according to the principles of the presentinvention;

FIG. 1-B shows electrostrictive elements arranged on segments of aninterventional device designed according to the principles of thepresent invention;

FIG. 2 is a flow-chart of the navigation process for a guide catheternavigation and placement and subsequent navigation of an interventionaldevice through and beyond the guide catheter;

FIG. 3 is a side elevation view of a portion of one embodiment of amedical device comprising one electrostrictive element according to theprinciples disclosed in the present application;

FIG. 4 is a side elevation view of a portion of a second embodiment of amedical device comprising a plurality of electrostrictive elementsdisposed around part of the device circumference;

FIG. 5 is a side elevation view of a portion of a third embodiment of amedical device comprising a plurality of electrostrictive elements fordeployment of a stent;

FIG. 6 is a side elevation view of a portion of a fourth embodiment of amedical device with two electrostrictive elements mechanically in seriesbut electrically in parallel;

FIG. 7 is a side elevation view of a portion of a fifth embodiment of amedical device comprising a plurality of electrostrictive elementsarranged along part of the length of the medical device according to theprinciples disclosed in the present application;

FIG. 8 shows application of the principles of the present invention todevice prolapse prevention;

FIG. 9 shows application of the principles of the present invention todevice dislodgment prevention;

FIG. 10 presents an application of the principles of the presentinvention to the treatment of left atrium atrial fibrillation; and

FIG. 11 illustrates application of the principles of the presentinvention to lung navigation.

Throughout the drawings, corresponding reference numerals indicate likeor corresponding parts and features.

DETAILED DESCRIPTION OF THE INVENTION

The various embodiments provide for devices and methods of enhancedmagnetic navigation of a medical device within a subject's body throughthe use of electrostrictive behavior. Electrostrictive behavior providesan additional means of controlling a segment of a medical device (e.g.catheter, endoscope, guide wire, guide catheter, sheath, or electrode)for navigation in the body. Electrostrictive materials are those inwhich application of a voltage will result in a dimension change(expansion or contraction, depending on the material). The effect ofapplying a voltage difference to an electrostrictive material is notinverted by inverting the voltage polarity, as opposed to piezoelectricmaterials. The arrangement of electrostrictive material on the medicaldevice provides for their use in deflecting the medical device distalend for navigational purposes. Electrostrictive control requiresapplication of a controlling variable from an external electrical powersource(s) to the segment electrostrictive components, to create thedesired strains and consequent bending or stiffening of the medicaldevice. The control variables may be a voltage or current applied to oneor more electrostrictive elements or piezoelectric elements disposed inthe medical device. The distal tip of a medical device may includeelectrostrictive polymers, for example, which when contracted causedeflection of the distal tip. The electrostrictive component isconnected to electrical leads that extend from the proximal end to thedistal end of the medical device.

An elongated navigable medical device 150 having a proximal end 152 anda distal end 154 is provided for use in an interventional system 100,FIG. 1-A. A patient 140 is positioned within the interventional system,and the medical device is inserted into a blood vessel of the patientand navigated to an intervention volume 180. In magnetic navigation amagnetic field externally generated by magnet(s) 170 orients a smallmagnet located at the device distal end (172, FIG. 1-B). Real timeinformation is provided to the physician, for example by an x-rayimaging chain 120 comprising an x-ray tube 122 and an x-ray detector124, and also possibly by use of a three-dimensional device localizationsystem such as a set of electromagnetic transmitters/emitters located atthe device distal end (not shown) and associated externalelectromagnetic receivers, or other localization device with similareffect. The physician provides inputs to the navigation system through anavigation computer 110 comprising user interface devices such as adisplay system 112, a keyboard 102, mouse 104, joystick 106, and similarinput devices. Display 112 also shows real-time image informationacquired by the imaging chain 120 and the three-dimensional localizationsystem. Computer 110 relays inputs from the user or from a controlcomputer imbedded in navigation computer 110 to a controller 130 thatdetermines and actuates the magnet(s) orientation through articulationcontrol 160. As shown in FIG. 1-B, electrostrictive element(s) 164located along the device length are activated to help in navigation, forexample by bending or stiffening the device. Electrostriction controller192 communicates with navigation computer 110, and also with thephysician through the user interface previously described, and controlsthe application of control voltages to the electrostrictive element(s).In specific embodiments, device tip 154 also has sensor(s) (not shown),such as strain gauges or similar devices located at or near the devicetip to provide force data information to estimate the amount of pressureapplied on the target tissue 190, as feedback to system 100 in assistingnavigation; other sensors might include an ultrasound device or otherdevice appropriate for the determination of distance from the device tipto the tissue. Yet other force sensors may be provided along variousdevice segments to measure the amount of force exerted by the subject'stissues onto the device. Such sensors signals including feedback datafrom the tip element and the device distal end are processed by feedbackblock 194 which in turn communicates with the electrostrictive controlblock 192 as well as with computer 110 comprising a control computer.Further device tip feedback data include relative tip and tissuepositional information provided by an imaging system, predictive devicemodeling, or device localization system. In closed loop implementation,the electrostrictive control 192 automatically provides input commandsto the device electrostrictive elements based on feedback data andpreviously provided input instructions; in semi-closed loopimplementations, the physician fine-tunes the navigation control, basedin part upon feedback data. Control commands and feedback data may becommunicated from the user interface and control 192 to the device andfrom the device back to the feedback block 194, through cables or othermeans, such as wireless communications and interfaces. As known in theart, system 100 comprises an electromechanical device advancer (notshown), capable of precise device advance and retraction based oncorresponding control commands.

In another aspect of the invention, a method is disclosed that enableselectrostriction-assisted magnetic navigation of an interventionaldevice to a theater of operation and subsequent acquisition ofdiagnostic information and/or treatment of specific conditions. FIG. 2provides a flowchart for an exemplary embodiment of the method. In thisapplication, the objective of the intervention is the treatment of acoronary occlusion, such as a chronic total occlusion. The interventionproceeds in three steps, first insertion of a guide catheter through thevasculature to the coronary ostium, followed by insertion of aninterventional device through the guide catheter to the occlusion, andthird treatment at the site of occlusion. The two navigation steps aredepicted in FIG. 2. First, the guide catheter is inserted in thesubject's body, 210. Magnetic navigation is initiated, guiding thedistal guide catheter tip in a series of steps with concurrent orsubsequent proximal device advance, 220. Next, the guide catheter tip ispositioned at the coronary ostium, 230. To prevent dislodgement, asoften occurs when inserting an interventional device through the guidecatheter, selective guide catheter stiffening is effected throughelectrostrictive actuation of specific elements on the guide catheter,240. In step 242, it is confirmed that the guide catheter is firmly inplace at the ostium. If not, 244, the method iterates through steps 230and 240 to attain this objective, and then proceeds, 250, to the secondnavigation sequence. In the next step, the interventional device isinserted through the guide catheter to the ostium, 260. Then theinterventional device is advanced and navigated, 270, beyond the guidecatheter distal end and through the coronary artery toward theocclusion. If the magnetic navigation is successful, 274, the methodproceeds to the third step, 286, performance of the treatment at theintervention site. Otherwise, 280, the interventional device is bent orstiffened by electrostriction of selected elements as necessary tofacilitate navigation to the occlusion, 282. Once a difficult turn oradvance has been made, magnetic navigation resumes 284, and these stepsare iterated 285 till the interventional device is successfullypositioned at the site of treatment, treatment takes place 286, and themethod terminates, 290.

In a first embodiment of a medical device 300 shown in FIG. 3, at leastone electrostrictive element 310 is disposed on a portion or side of thedistal end 304 of the medical device 300. The electrostrictive element310 is adapted to cause the distal end 304 to bend in a given direction.Electrical energy transmitted through fine wires 312 extending along thelength of the medical device 300 from the proximal end 302 activatespiezoelectric or electrostrictive actuator elements. Although wires andelectrostrictive elements are shown for illustration as being externalto the device 300 structure, it is understood that preferably element310 is embedded within the device wall or within the device so that itdoes not protrude externally; and similarly wires 312 run within thedevice wall or lumen. A similar remark applies to FIGS. 4 to 7. Theapplication of an electric potential across the electrostrictive element310 causes the electrostrictive element 310 to change dimension, in turncausing the medical device 300 to bend. The bending action at the wallcould occur either because the device 300 itself would bend uponapplication of voltage, or by affixing an element 310 to another elementwhich could bend but not stretch or compress. The medical device 300could then be twisted at the proximal end 302 to effect a turn in anydirection. The deflection or manipulation of such a medical device 300would be somewhat limited however, in particular as torque applied atthe device proximal end does not always propagate effectively to thedistal end. The medical device 300 may be used in combination with adelivery sheath (not shown) that comprises at least one magneticallyresponsive element on or near its distal end. The magneticallyresponsive element disposed on the distal end of the delivery sheath maybe oriented in a desired direction by application of a magnetic field,which aligns the magnetically responsive element with the fielddirection. Accordingly, the delivery sheath may be magneticallynavigated though a subject's body by changing the direction of anapplied magnetic field that is applied to the subject's body in whichthe delivery sheath is introduced. Conversely, electrostrictive elementsmay be placed along the length of a delivery sheath, while a catheter orother medical device designed to be inserted through the delivery sheathmay be magnetically guided, at least when advancing beyond the distalend of the delivery sheath. Generally speaking, magnetic andelectrostrictive elements may be placed by themselves or in combinationalong any portion of a medical device; the medical device being one of aguide catheter, catheter, sheath, guide wire, interventional device,endoscope, surgery device, or any interventional medical device designedto be inserted in a subject's body cavity.

Where a delivery sheath, guide catheter, or similar interventionaldevice encounters' difficulty during magnetic navigation, the medicaldevice 300 may be employed in combination with the delivery sheath fornavigating towards a target area within the subject's body. Oneembodiment of a method is provided for navigating such a medical device300 in the body. The method comprises magnetically navigating a deliverysheath to a selected orientation by applying a magnetic field to orienta magnetically responsive element in the distal end portion of thesheath, and advancing the sheath. The method further provides foradvancing the distal end of a flexible medical device 300 within thedelivery sheath from the distal end of the delivery sheath. By applyinga voltage to at least one electrostrictive element 310 on the flexiblemedical device 300, the distal end 304 of the medical device 300 may bechanged in shape, to guide the medical device 300 (and also possibly thedelivery sheath) in a selected direction. Conversely, a delivery sheath,guide catheter, or similar interventional device might be navigated byactuating electrostrictive elements placed thereon, while a catheter orother medical device designed to be inserted through the delivery sheathmaybe magnetically guided, at least when advancing beyond the distal endof the delivery sheath.

A preferred embodiment of a medical device might comprise a plurality ofelectrostrictive elements 410 affixed about a circumference of theexterior of the medical device 400 as in FIG. 4. Combinations ofvoltages applied to the electrostrictive elements 410 could then deflectthe distal end 404 of the medical device 400 in any direction withoutrequiring twisting the proximal end 402. In a second embodiment of amedical device 400, the medical device 400 comprises at least twoelectrostrictive elements 410 disposed on a portion or side of thedistal end 404 of the medical device 400, causing the distal end 404 tobend in a given direction. Symmetric placements of a multiplicity ofsuch elements around the device circumference can provide bendingcapability in a range of bending planes or across several bendingplanes.

The medical device 400 may further comprise at least one magneticallyresponsive element 440 on or near the distal end portion 404. Themagnetically responsive element 440 disposed on the distal end portion404 of the medical device 400 may be oriented in the direction of anexternally applied magnetic field. Accordingly, the medical device 400may be magnetically navigated though a subjects body by changing thedirection of an applied magnetic field to guide the medical device 400.Likewise, a magnetically navigable delivery sheath may be used incombination with the medical device. The delivery sheath preferablycomprises at least one electrostrictive element disposed on a portion orside of the distal end of the sheath, for causing the distal end to bendin a given direction.

Accordingly, at least one embodiment of a method for navigating such amedical device 400 and a delivery sheath, guide catheter, or similarinterventional device within a subject's body is provided. The methodprovides for electrostrictively navigating a delivery sheath to aselected orientation by applying a voltage to one or moreelectrostrictive elements on the sheath to orient the distal end portionof the sheath and advancing the sheath, and advancing the distal end ofa flexible medical device 400 from the distal end of the sheath, andapplying a magnetic field to orient a magnetically responsive element440 in the distal end portion 404 of the device 400 to orient the distalend of the medical device 400 in a selected direction. The method mayfurther comprise applying a voltage to at least one electrostrictiveelement 410 to cause the distal end 404 to bend in a select direction.

With the second embodiment of a medical device 400, a method fornavigating the medical device 400 within a subject's body without theuse of a delivery sheath is also provided. The method comprisessuccessively orienting the distal end 404 of the medical device 400 byapplying a magnetic field to orient a magnetically responsive element440 in the distal end portion 404 of the device 400. The method furthercomprises applying a voltage to at least one electrostrictive element410 on the medical device 400 to change the orientation of the distalend 404 from the orientation achieved by the application of the magneticfield alone. Thus, the medical device 400 may be advanced upon achievingthe desired orientation of the distal end 404 using the above methods. Amethod is also provided for navigating the medical device 400 in whichthe medical device 400 may be selectively stiffened to assist inadvancing or pushing the medical device 400 through the subject's body.In this embodiment of a method for navigation, the method of navigatingcomprises orienting the distal end 404 of the medical device 400 byapplying a magnetic field to orient a magnetically responsive element420 in the distal end portion 404 of the device 400. The method furthercomprises advancing the device 400, and applying a voltage to at leastone electrostrictive element 410 on the device 400 to selectivelystiffen a portion of the medical device 400.

Similarly, an improved method of magnetically navigating a medicaldevice 400 having at least one magnetically responsive element 440 andat least one electrostrictive element 410 disposed on or near the distalend portion 404 of the device 400 is provided. The method comprisessuccessively orienting the distal end 404 of the medical device 400 byapplying a magnetic field to orient a magnetically responsive element440 in the distal end portion of the device 400. The method furthercomprises applying a voltage to the at least one electrostrictiveelement 410 of the medical device 400 to selectively shape a portion ofthe medical device 400 to change the orientation achieved by theapplication of the magnetic field alone. Accordingly, the medical device400 may be advanced upon orienting the distal end 404 of the medicaldevice 400 by utilizing the magnetically responsive element 440, theelectrostrictive element 410, or both.

A stent catheter for delivering a stent 530 in the body may also be usedin accordance with the principles of the present invention. In a thirdembodiment of a medical device, the device is a stent catheter 500including a landing for supporting a stent 530 thereon, and at least oneelectrostrictive element 510 in the landing to facilitate bending of thecatheter 500 in the vicinity of the landing upon application of avoltage to the electrostrictive element 510.

Accordingly, a method of placing a stent 530 in the vasculature of asubject is provided. The method of placing a stent 530 in thevasculature in a subject comprises navigating the distal end 504 of acatheter 500 carrying the stent 530 through the vasculature by operatingone or more actuators 510 to orient the distal end portion 504 of thecatheter 500, and advancing the catheter. The catheter 500 may compriseone or more electrostrictive actuator elements 510 under the stent 530which may be actuated together to facilitate bending of the catheter 500and stent 530. The one or more actuators 510 may be operated by applyingvoltage to at least one electrostrictive actuator element 510 on thecatheter 500. In another embodiment of a method of placing a stent 530in the vasculature in a subject, the method comprises navigating thedistal end 504 of a stent delivery catheter 500 carrying the stentthrough the vasculature by applying a magnetic field to orient amagnetically responsive element (not shown) on the distal end portion ofthe catheter 500. The method may further comprise applying a voltage toat least one electrostrictive element 510 to facilitate the bending ofthe catheter 500 and stent 530. Thus, the medical device 500 may beadvanced upon orienting the distal end 504 of the medical device 500 byemploying the magnetically responsive element, the electrostrictiveelement 510, or both.

In a fourth embodiment of a magnetically navigable medical device shownin FIG. 6, the medical device 600 comprises a plurality ofelectrostrictive elements 610 disposed on or near the distal end portion604, and a plurality of contact sensors 620 disposed on or near thedistal end portion 604, or near electrostrictive element(s) 610. Themedical device 600 includes at least one magnetically responsive element640 associated with the distal end 604 of the device 600, which mayorient the device 600 upon application of a magnetic field in a selecteddirection. The magnetically responsive element 640 is of a sufficientsize, shape, and magnetic characteristics to cause the distal end 604 ofthe medical device 600 to be oriented in a selected direction inresponse to an applied magnetic field of preferably no more than about0.1 Tesla, and more preferably no more than about 0.08 Tesla, and morepreferably no more than about 0.06 Tesla.

When actuated, the electrostrictive elements 610 change the flexibilityor shape of the medical device. In the particular embodimentillustrated, the electrostrictive elements 610 may act mechanically inseries, but are electrically in parallel for actuating eachelectrostrictive element as shown in FIG. 6. This configurationincreases the total bend angle that could be attained for a givenvoltage application.

Accordingly, a method of navigating an elongated medical device isprovided, whereby navigation is effected through a combination ofmagnetic navigation and selective electrostrictive bending or stiffeningof at least a device segment. Electrostrictive actuation is determinedby the user, a control computer based on input instructions, or a useror control computer based on feedback from contact sensor(s).Application of electrostrictive bending or stiffening serves to controlthe amount of contact force between part of the device and the vessel orbody cavity wail.

In a fifth embodiment of a medical device shown in FIG. 7, the medicaldevice 700 comprises a plurality of electrostrictive elements 710 alongat least a segment of the medical device. Several of theelectrostrictive actuating elements 710 may be electrically connected inparallel to each other, and several of the electrostrictive actuatingelements 710 may be connected in series. The plurality ofelectrostrictive elements 710 may comprise a plurality of embeddedelectrostrictive actuating members that are embedded within the outerportion or within the wall of the elongate medical device 700. A usefularrangement of elements might act not at a single location along acatheter, but instead may comprise one or more strip(s) of elementsalong a side of a device as shown in FIG. 7. Each element 710 of thestrip is mechanically in series with a next element 710 of the samestrip, but may be electrically connected in parallel or in series. Usingone or more strips, as in FIG. 7, would provide for more effectivebending or turning of the medical device 700. The construction of suchstrips might take advantage of methods used in the semiconductorindustry. In this embodiment various electrostrictive elements mighthave various transfer functions (ratio of bend to applied voltage) alongeach strip so as to provide for a non-uniform bending of a medicaldevice 700 having a uniform bending stiffness. The same effect could beachieved with a medical device 700 of variable stiffness and strips ofuniformly responsive electrostrictive elements 710; that configurationmight be undesirable for medical reasons in specific applications. Theplurality of strips having electrostrictive actuating elements 710 maybe connected in at least two groups, each of which when actuated causesthe medical device 700 to assume a predetermined configuration.

Accordingly, an improved method for navigating a medical device 700having at least one magnetically responsive element 740 and a pluralityof electrostrictive elements 710 is also provided. The improved methodcomprises using an externally applied magnetic field of no more thanabout 0.1 Tesla, and more preferably no more than about 0.08 Tesla, andmore preferably no more than about 0.06 Tesla, to orient themagnetically responsive element 740 and the distal end 704 of themedical device 700. The method further comprises applying a voltage toat least one electrostrictive element 710 on the device 700 to changethe orientation of the distal end 704 of the medical device 700 if themagnetic field is insufficient to orient the device 700 in the desireddirection. Thus, the method also provides for improved navigation of amagnetically navigable medical device 700 with application of magneticfields of reduced magnitude to the subject's body. The method alsoprovides for improved navigation in magnetic fields of variousmagnitudes, by allowing design of reduced size magnetic tips that moreeasily navigate convoluted anatomy or narrow lumen. Similarly, animproved method of navigating a medical device 700 in an externallyapplied magnetic field is provided, by applying a voltage to at leastone electrostrictive element 710 to change the orientation of themedical device 700 in a direction of which the magnetic field is notable to attain. An example of such a direction is one having a componentparallel to a “forbidden plane” of a magnetic navigation system. Whenattempting to perform magnetic navigation using a Magnetic ResonanceImaging (MRI) system, the main static field is typically oriented alongthe patient's longitudinal axis. A device tip located for example in aplane orthogonal to the static field axis (the forbidden plane), cannotbe re-oriented in that plane by using the static magnetic field alone;indeed the torque applied by the static field is always orthogonal tothe field axis, and therefore cannot induce rotation around the staticfield axis. Use of electrostrictive orientation allows navigation insuch a system, including navigation in the forbidden plane.

In each of the above embodiments of a medical device, little energy isrequired in electrostrictive activity (current only flows while themolecular constituents achieve their strained condition or whilechanging the strained condition). Fine wires can be used, and oneskilled in electromagnetism would know how to insulate them so thatvoltages would not cause arcing or otherwise endanger a patient.Furthermore, the wires may be embedded within the side of the medicaldevice, or may extend through a lumen within the medical device to theproximal end of the device. Likewise, by appropriate design as known inthe art, application of electrical energy to the electrostrictiveelements does not affect any sensors that may be employed within thesubject's body.

In the fifth embodiment discussed above, the magnetically navigableelongate medical device 700 may further include a plurality of contactsensors 720 for sensing contact of the medical device 700 with a tissuewall. The contact sensors 720 may be stress sensors that detect a forceacting on the medical device, and provide an output indicative of thelevel of force. The contact sensors 720 may also be strain gauges thatdetect deflection of the distal portion 704 of the medical device 700upon contacting a surface within a subject's body. In the magneticallynavigable elongate medical device 700, the signals associated with thesensing and actuating elements are connected by fine wires (not shown)embedded in a non-conducting material on the medical device. The sensors720 of the medical device 700 enable sensing of contact along a portionof the medical device 700 with a tissue surface within the subject'sbody, such that an electrostrictive element 710 disposed along thatportion of the medical device 700 may be actuated to stiffen oralternatively bend the portion that has been contacted. The sensors 720accordingly allow for controlling or minimizing the amount of deflectionof the medical device 700 caused by contact along a portion of thedevice with a tissue surface within the subjects body.

Accordingly, an improved method of navigating such a medical device 700having a plurality of electrostrictive elements 710 and a plurality ofsensors 720 is provided. The method provides controlling anelectrostrictively actuated elongate medical device 700 by actuating oneor more of the electrostrictive elements 710 in response to a signalfrom a contact sensor 720, to selectively stiffen or alternatively bendthe medical device 700 in the vicinity of the sensed contact. Otherembodiments of the method may further control the contact between thedistal end 704 of an elongate medical device 700 and a moving anatomicalsurface, such as a beating heart wall or an expanding lung wall. Themethod comprises applying a time-varying voltage to at least oneelectrostrictive element 710 on the medical device 700 to change theconfiguration of the medical device 700 as the anatomical surface moves,to maintain contact between the medical device 700 and the surface.Where the anatomical surface is the surface of the heart, theapplication of voltage may be gated with an electrocardiogram signalsuch that the electrostrictive element 710 is actuated as the heartbeats to bend the distal end portion 704 to maintain contact of themedical device 700 against the heart surface.

In yet another embodiment of a method in accordance with the principlesof the present invention, a method for circumscribing a path of contacton a tissue surface is provided. In one or more of the afore mentionedembodiments of a medical device 700 having at least one electrostrictiveelement 710, a method is provided for establishing contact with ananatomical surface in a ring pattern. The method comprises magneticallyorienting an elongate medical device 700 toward the center of anintended circle of contact on a tissue surface, and applying a voltageto at least one electrostrictive element 710 near the device 700 distalend. The activation of the electrostrictive element 710 causes themedical device 700 to deflect or bend into a position of contact withthe tissue surface. The medical device 700 may either be rotated byproximal torque application to circumscribe a circle about thelongitudinal axis of the medical device 700, or a plurality ofelectrostrictive elements 710 disposed around the axis of the medicaldevice 700 may be alternately actuated to cause the device distal end tocircumscribe a circle or arc of a circle about the initial distallongitudinal axis of the medical device. Alternatively, a method forcontacting an anatomical surface in a ring pattern or arcs of a ringpattern is provided that includes orienting an elongate medical device700 relative to the center of the ring by applying a voltage to at leastone electrostrictive element 710 on the elongate medical device, andswinging or rotating the medical device about an arc by applying achanging magnetic field to the depending device tip to magneticallyorient a magnetically responsive element 740 carried thereon, orapplying torque at the device proximal end, or combinations thereof.

A medical device and navigation system combination is also provided forcontrolling the navigation of the medical device within a subject'sbody. The combination generally comprises an elongate medical devicedesigned for magnetic navigation having a plurality of electrostrictiveelements for selectively stiffening or bending portions of the device,and a plurality of contact sensors for sensing contact with the medicaldevice. The combination further comprises a control for actuating one ormore of the electrostrictive elements in response to a signal from acontact sensor, to selectively stiffen or bend a portion of the medicaldevice in the vicinity of the sensed contact. The combination furthercomprises the use of magnets located at least at the device tip. Thecombination may employ any of the afore-mentioned embodiments of amedical device. The electrical connections to the electrostrictiveelements and sensors of the medical device are in communication with thecontrol via one or more connections, for enabling the feedback andcontrol blocks to sense contact signals and to apply electrical signalsto the electrostrictive elements. Alternatively, sensors data areprovided through wireless connection, and power is supplied to thedevice by a power supply attached to the device proximal end. Thecombination of a medical device and navigation system accordinglyfacilitates stiffening a portion of the medical device to minimize thedeflection of the medical device caused by contact with a tissuesurface, enhances the ability to deflect the medical device to reach orcontact a target area within the body, decreases device prolapse anddislodgement, and increases maneuverability.

FIG. 8 illustrates application of the devices and methods of the presentinvention to interventional medical device prolapse prevention. Incertain situations schematically represented by numeral 800, aninterventional device 806 may have been magnetically navigated usingexternally generated magnetic field B 816 past a vessel confluence 820.The device distal tip 804 then encounters resistance to advancement; inFIG. 8 this resistance is due to an occlusion that needs to be traversedfor therapy to be effective. Device design typically requires atrade-off between flexibility for maneuverability and stiffness toenable effective device advancement as well as proximally applied torquepropagation. However, as mechanical force is proximally applied toadvance the distal tip through the lesion, a device segment mightprolapse into vessel branch 822. Under such condition, advancement forceis no longer effectively transmitted to the distal tip but instead leadsto further device prolapse. To prevent this, one or a plurality ofelectrostrictive elements 810 placed along the device length areactuated to stiffen the device segment located at or near the vesselbifurcation. Stiffening at the confluence reduces device flexibility,prevents prolapse, and enables force application at the lesion 824 alonglocal vessel axis 826.

Similarly, FIG. 9 illustrates schematically how selective devicestiffening could prevent dislodgment. A medical device such as a guidecatheter 902 is navigated through a chamber or body cavity 910 such thatthe guide catheter distal tip 204 is engaged at least partially invessel or body lumen 920. The guide catheter distal end in the proximityof the lumen is curved such that upon advancement of an interventionaldevice such as a catheter 930 a mechanical force is acted upon the guidecatheter with a force component 934 orthogonal to the local guidecatheter axis. This force component might dislodge the guide catheterdistal tip 904 from the lumen, creating intervention complications anddelays. Actuation of electrostrictive components 940 located at or nearthe guide catheter bend to stiffen the device, by themselves or incombination with other actions such as distal guide catheter forceapplication, will prevent device dislodgment and thus improveintervention effectiveness and efficacy. Alternatively, dislodgment mayoccur due to motion of the beating heart; there again selective devicestiffening by itself or in conjunction with distal guide catheter forceapplication will be effective in preventing wall motion and/or flow todislodge the device. Dislodgement may also occur when an interventionaldevice is inserted through the guide catheter and progresses beyond theguide catheter distal end, and resistance to advancement is encountered;selective stiffening and/or bending of the guide catheter is effectivein preventing resistance to result in guide catheter dislodgment.

FIG. 10 schematically presents application of the principles of theinvention to the treatment of left atrial fibrillation, 1000. For such aprocedure, the catheter 1002 is navigated through aorta 1010 into theleft ventricle 1020, and then through the mitral valve 1030 and into theleft atrium 1040. From the left atrium, it must be possible to addressspecific points with the device distal end 1004. Often it is desirablefor the ablation pattern to be applied on an arc of a circle around atleast one of the pulmonary veins 1050, for fibrillation to beeffectively treated. Thus, non-surgical cure for atrial fibrillation isgreatly facilitated by improved navigation through convoluted lumen,chambers and valves, selective catheter stiffening, and enhanced distaltip orientation and control in the left atrium, as enabled by thedevices and methods of the present invention.

FIG. 11 schematically illustrates application of the devices and methodsof the present invention to lung bronchial navigation. An interventionaldevice, such as a catheter or bronchioscope 1106, is inserted into thesubject's airways and through the trachea 1112, about 20 to 25 mm indiameter. To reach a remote lung nodule or alveoli, the device isnavigated through a series of passageways of reducing diameter. Insuccession after the trachea are the root bronchi (either left orright), followed by the segment bronchi (about 7 mm diameter), thatsubdivide in the course of seven to eight steps into bronchioles withina specific lobe (with a decreasing diameter from 5 mm to 1 mm). Thebronchioles then lead to the membranous lobules and after two or threesubdivisions lead to the terminal bronchi. Navigation requires multiplebranch decisions, and as such is enabled or greatly facilitated bymagnetic steering as known in the art. However, the interventionaldevice has to progress through lumens or widely varying diameter;accordingly it is difficult to proximally transmit forces and torqueswhen advancing the device. There is a tendency for the device to bend,loop, or even prolapse into one of the main lung branches that are notpart of the navigation path. The device and method of the presentinvention provide for selective segment bending or stiffening 1130 ofthe device through electrostrictive actuators (not shown). Suchactuators may be provided substantially along the length of the inserteddevice, or at least over a length extending proximally to a givendistance of the distal tip.

Alternatively or additionally, in one embodiment of the presentinvention, one or a plurality of piezoelectric elements are imbeddedalong the length of a medical device. Such elements respondalgebraically to tension and compression, and accordingly distinguishbetween the two states based on an induced voltage polarity. Imbeddingpiezoelectric elements enable shape feedback and provides and indicationof both the amount of local device tensioning and/or bending as well asbending direction. In closed-loop device navigation, the local shapefeedback information is taken into account in applying device deflectionor actuation means, such as mechanical pull-wires tension, appliedelectrostrictive tension, applied magnetic fields or magnetic fieldgradients, and other such device deflection means as known in the art.In particular, the placement of piezoelectric elements in the directvicinity of medical device deflection or actuation elements permitsaccurate feedback and more precise navigation control.

In one preferred embodiment, local tension or compression feedbackinformation is leveraged by a virtual device model that predicts theactual device shape under the measured applied tension and compressionforces. The use of such a virtual model in conjunction withpiezoelectric and electrostrictive devices, enable improved moreaccurate navigation while limiting the number of such measurement andcontrol devices. When used in combination with additional devicenavigation means, such as mechanical pull wires and/or magneticdeflection, virtual models provide visual feedback to the user andeliminate much of the “guess work” associated with navigating withoutsuch means. Virtual models enable user anticipation of the result oftheir navigation control commands as well as faster decision withrespect to a course of actions to take to achieve a particularnavigation diagnostic or therapeutic goal.

Although the present invention has been described with respect toseveral exemplary embodiments, there are many other variations of theabove-described embodiments that will be apparent to those skilled inthe art, even where elements have not explicitly been designated asexemplary. It is understood that these modifications are within theteaching of the present invention, which is to be limited only by theclaims appended hereto.

1. A method of performing a medical intervention in a subject's body,the method comprising navigation of at least one medical devicecomprising several segments through the body lumens or cavities, thenavigation method comprising the step of applying a magnetic field toorient a magnetically responsive element in the distal end portion ofthe device and advancing the device, and further comprising at least onenavigation step selected from the group consisting of i) bending aportion of a medical device through electrostriction; ii) stiffening asegment of a medical device through electrostriction; and iii) rotatinga segment of a medical device through electrostriction.
 2. The method ofclaim 1, wherein magnetic actuation and the at least one othernavigation step occur at different times.
 3. The method of claim 1,wherein magnetic actuation and the at least one other navigation stepoccur simultaneously.
 4. The method of claim 1, wherein magneticactuation and the at least one other navigation step are applied to atleast two different medical devices used in sequence or concurrently. 5.(canceled)
 6. The method of claim 4, wherein at least one device isnavigated using only one navigation step.
 7. The method of claim 1,further comprising: i) guiding the device through a lumen bifurcation;and ii) selectively stiffening a device segment through actuation of atleast one electrostrictive element at or near the vessel bifurcation. 8.The method of claim 1, further comprising: i) guiding the device distalend through a cavity or chamber to a lumen ostium; and ii) selectivelystiffening a device segment through actuation of at least oneelectrostrictive element at or near the lumen ostium or within thecavity or chamber.
 9. The method of claim 1, further comprising: i)guiding the device distal end to contact a tissue wall; and ii)selectively stiffening a device segment through actuation of at leastone electrostrictive element at or near the device distal end tomaintain tissue contact during wall motion.
 10. The method of claim 1,wherein the step of applying a magnetic field comprises successivelyorienting the distal end of the medical device by applying a magneticfield to orient a magnetically responsive element in the distal endportion of the device, and advancing the device; and applying a voltageto at least one electrostrictive element located on the device to changethe orientation of the distal end from the orientation achieved by theapplication of the magnetic field alone.
 11. (canceled)
 12. (canceled)13. (canceled)
 14. (canceled)
 15. (canceled)
 16. (canceled) 17.(canceled)
 18. The method of claim 1, wherein the at least one medicaldevice comprises a catheter carrying a stent, and the step of applying amagnetic field comprises navigating the distal end of a cathetercarrying the stent through the vasculature by applying an externalmagnetic field to orient the distal end portion of the magneticallynavigable catheter and advancing the catheter, and the at least onenavigation step comprises applying a voltage to an electrostrictiveelement on the catheter to facilitate the bending of the catheter andstent.
 19. The method of claim 1, further comprising the step ofcontrolling the contact between the distal end of an elongate medicaldevice and a moving anatomical surface, the step of controlling thecontact comprising applying a voltage to an electrostrictive element onthe medical device to change the configuration of the medical device asthe anatomical surface moves to maintain contact between the medicaldevice and the surface.
 20. The method according to claim 19 wherein theanatomical surface is the surface of the heart, and wherein theapplicant of the voltage is gated with the electrocardiogram signal. 21.The method of claim 1, wherein the at least one navigation stepcomprises bending the medical device by applying a voltage to at leastone electrostrictive element on the device, which is effective to changethe orientation of the medical device to a direction having a componentin the plane orthogonal to the magnetic field direction.
 22. The methodof claim 1, wherein the step of applying a magnetic field comprisesusing an externally applied magnetic field of less than about 0.1 Teslato orient the distal end of a medical device by orienting a magneticallyresponsive element on the medical device, and the at least onenavigation step comprises bending the medical device by applying avoltage to at least one electrostrictive element on the device, which iseffective to change the orientation of the distal end of the medicaldevice if the magnetic field is insufficient to orient the device in thedesired direction.
 23. (canceled)
 24. (canceled)
 25. (canceled)
 26. Amedical device and navigation system combination comprising: an elongatemedical device having a plurality of electrostrictive elements forselectively stiffening portions of the device and a plurality of contactsensors for sensing contact with the medical device. a control foractuating one or more of the electrostrictive elements in response to asignal from a contact sensor, to selectively stiffen a portion of themedical device in the vicinity of the sensed contact.
 27. Thecombination according to claim 26 wherein the medical device includes atleast one magnetically responsive element associated with the distal endof the device, and further including orienting the device by applying amagnetic field to cause the distal end of the device to align in aselected direction.
 28. A magnetically navigable elongate medicaldevice, the device having a proximal end, and a distal end, andincluding at least one magnetically responsive element associated withthe distal tip of sufficient size and shape to orient the distal end ofthe medical device in a selected direction in response to an appliedmagnetic field, and a plurality of electrostrictive elements disposedbetween the proximal and distal ends, which when actuated, change theflexibility or shape of the medical device.
 29. The magneticallynavigable medical device according to claim 28, wherein the magneticallyresponsive element is of sufficient size and shape to align the medicaldevice in response to an applied field of 0.1 Tesia or less. 30.(canceled)
 31. (canceled)
 32. (canceled)
 33. (canceled)
 34. (canceled)35. The medical device of claim 1 wherein at least some of theelectrostrictive actuating elements are connected in parallel and atleast some of the electrostrictive actuating elements are connected inseries.
 36. The medical device of claim 1 wherein the electrostrictiveactuating elements are connected in at least two groups, each of whichwhen actuated causes the medical device to assume a predeterminedconfiguration.